1. Field of the Invention
The invention relates to distillation processes and apparatus and also to mineral oils, preparation, recovery or extraction from solid natural sources, and specifically to recovery from shale or bituminous sand. An aspect of the invention also relates to metallurgical apparatus, including means for treating ores or for extracting metals.
2. Description of the Prior Art
Petroleum products are recovered from shale or bituminous sands by retorting at approximately 900.degree. F. It is known to use closed retorts wherein a suitable source of heat vaporizes the carbonacous material known as Kerogen into gas and oil vapors, after which the vapors are condensed in a fractionating device. In order to control the heat supplied to the retort and prevent oxidation of the petroleum, a liquified metal may be interposed between the source of combustion and the shale. For this purpose lead has been used.
Further shale processing techniques include direct contact and immersion in molten baths of metal or salts. It has been proposed, for example, to introduce crushed shale into a molten bath of lead or lead-zinc from an inlet near the bottom of the bath, and then permit the shale to rise through the molten metal. Petroleum products are recovered as a vapor at the top of the bath and subsequently condensed, and the spent shale is discharged at the top of the bath as a waste product. Zinc has been used in combination with the lead in such a bath on the theory that gold, silver, and other precious metals from the shale can be recovered in dissolved form from the zinc. Other direct contact techniques simply place the shale on the top of a molten metal bath via a continuously operating conveyor belt that also continuously skins spent shale from the bath.
Lead and lead compounds or mixtures have been preferred because this metal has a liquid state between suitable temperatures, 800.degree. F. to 1000.degree. F., for petroleum recovery, and in addition, lead has a specific gravity sufficiently high that the spent shale is easily recovered from the upper surface of the bath. The possibility of employing lighter metals such as aluminum, lithium and sodium has been examined, but the difficulty of recovering the spent shale from the bottom of the metal bath presents a problem. A drawback to using a metal imersion bath is that coke-like products produced during the petroleum recovery process tend to be sticky and to adhere to the surface of the reaction vessel. It has been proposed to introduce an artificial swirling motion in a metal bath by pumping molten metal continuously into the bath and thereby discourage coke build-up on the vessel walls.